Nigh (2000) site index model for interior western redcedar (BC)

Implementation of the Nigh (2000) polymorphic site-index equation for interior western redcedar (THUJ.PLI).

Usage

si_nigh2000(age, height = NULL, si = NULL)

Arguments

age: Numeric vector. Breast-height age (years).
height: Optional numeric vector. Top height (m). If provided, `si` is predicted.
si: Optional numeric vector. Site index (m, base age 50 years at breast height). If provided, `height` is predicted.

Value

A tibble with columns:

height: Predicted top height (m), returned when input `si` is provided.
si: Predicted site index (m), returned when input `height` is provided.

Details

Species coverage: THUJ.PLI.

Geographic use: interior British Columbia.

Age definition note: `age` is breast-height age (years).

Base-age note: site index in this model is referenced to base age 50 years at breast height.

Provide exactly one of `height` or `si`:

If `height` is provided, the function predicts `si`.
If `si` is provided, the function predicts `height`.

Inputs/outputs are metric (m), matching the source model.

Predicting `height` from `si` is direct. Predicting `si` from `height` is implicit and solved numerically with `stats::uniroot()`.

References

Nigh, G. D. (2000). Western redcedar site index models for the interior of British Columbia. British Columbia Ministry of Forests, Research Report 18.

Examples

# Predict site index from age + height
si_nigh2000(
  age = c(25, 50, 90),
  height = c(9, 16, 27)
)
#> # A tibble: 3 × 1
#>      si
#>   <dbl>
#> 1  17.3
#> 2  16  
#> 3  17.3

# Predict height from age + site index
si_nigh2000(
  age = c(25, 50, 90),
  si = c(12, 16, 22)
)
#> # A tibble: 3 × 1
#>   height
#>    <dbl>
#> 1   6.10
#> 2  16   
#> 3  32.6